What am I ?

1. I am the tallest animal in the world . I live in the grassland of Africa . I feed in tall trees and spend at least 12 hours per day eating . The pattern on my body helps me hide from my enemies . I have three horns and excellent eyesight and hearing . When attacked , i defend myself by kicking me enemy with my heavy hoofs . I usually sleep standing up , so i can make a quick getaway if i need to .

2. i live on the plains of Africa . One of my ancestors was the largest land mammal that ever lived . People spread rumors about how violent i am , but i am actually very peaceful unless i am forced my horn , i am now a protected animal , due to the diminishing population of my species .

Please answer the question :" what am i ? "